That's not how you express that in Arabic. You would rather say: هل الأسعار غالِية في ولايته or هل المعيشة غالية في ولايته
We, in Lebanon, would express it that way quite naturally. The makers of the course are trying to include sprinkles of dialects in the course to teach useful every day language. They're not trying to teach pure MSA here. They're trying to strike a balance between MSA and spoken language. As they mentioned in an article linked during the course launch:
we’re teaching a less-formal, spoken version of Modern Standard Arabic — not the version that would appear in poetry or formal news broadcasts, but instead the version that would be used once a newscaster stopped reading from their script and started talking to their interviewee. It’s a version of the language that can be used in a formal conversation, but one that also can be used with the widest range of Arabic speakers.
You can read their full article here https://making.duolingo.com/what-makes-arabic-hard-and-why-that-shouldnt-stop-you-from-learning-it